Novel Zr-modified nano-CaO sorbents with cage-like hollow sphere structure were prepared for increasing the durability of CO 2 sorption via an ion precipitation method using carbon spheres as a template. A thorough study on the influence of the Ca/Zr molar ratio and the effect of cage-like structure on the CO 2 sorption durability of the prepared sorbents was performed using thermogravimetric analysis. It was found that the optimum Ca/Zr molar ratio of 5 maintained the most favorable CO 2 sorption stability, which maintained a CaO conversion of 76% after 30 cycles, whereas the CaO conversion of a nano-CaO cage-like hollow sphere sorbent without Zrmodification decayed to 20%. The combination of the Zr-modification and the cage-like structure demonstrates a synergistic effect in enhancing the CaO conversion and sorption stability due to the formation of CaZrO 3 with a cagelike porous structure, which facilitated CO 2 diffusion and minimized thermal sintering. Furthermore, a detailed comparison was made among the Zr-, Mgand Al-stabilizers. It was found that the Zr-stabilized sorbents exhibited better durability than that of Al-and Mg-stabilized sorbents due to the formation of CaZrO 3 with a high Tammann temperature (T T ).

Cage-like nano-CaCO 3 hollow spheres with different cavity diameters for CO 2 sorption were prepared using the template-directed synthesis method. Carbon sphere templates with different diameters were synthesized via a hydrothermal reaction of starch under variable conditions. Field emission scanning electron microscopy (SEM) and transmission electron microscope (TEM) images indicated that the synthesized cage-like nano-CaCO 3 hollow spheres had different cavity diameters of 0.52 µm, 1.62 µm and 2.93 µm. The hollow spheres shells were composed of many uniform nanoparticles with diameters of approximately 80 nm, as supported by the X-ray diffraction (XRD) results. Furthermore, the CO 2 sorption properties of the cage-like nano-CaCO 3 hollow spheres were analyzed by thermo-gravimetric analysis (TGA).The sorption capacity of the optimum sample with a diameter of 1.62 µm reached the 0.786 g CO2 g CaO -1 at 600 °C and exceeded the sorption capacity of the reference nano-CaCO 3 sorbents by 45 %. The sorption properties of the sample within the rapid reaction stage at the different temperatures of 550 °C, 600 °C and 650 °C were also evaluated. The results demonstrated that the sample exhibited a 30 % higher sorption rate than nano-CaCO 3 . Therefore, cage-like nano-CaCO 3 hollow spheres possess enhanced CO 2 sorption capacity and higher sorption rates.

Preparation of MgO-coated nano CaO using adsorption phase reaction technique for CO2 sorption.